The implication is that subsequent calls to
Zend\Session\SessionManager#start() (in later requests, assuming a session was
created) will not have any validator metadata attached, which causes any
validator metadata to be re-built from scratch, thus marking the session as
valid.

An attacker is thus able to simply ignore session validators such as RemoteAddr
or HttpUserAgent, since the "signature" that these validators check against is
not being stored in the session.

Action Taken

We now store the signature of the validators in the session immediately
following the call to session_start(), preventing any data loss from session
validators.

The patch fixing the issue has been applied in the following versions:

Zend Framework 2.2.9

Zend Framework 2.3.4

Recommendations

If you are using session validators, we recommend upgrading immediately.

Other Information

Acknowledgments

The Zend Framework team thanks the following for identifying the issues and
working with us to help protect its users: